1. Field of the Invention
The present invention generally relates to electro-optical readers, such as scanners and imagers, for reading codes and, more particularly, to a cordless reader which can operate when moved between cold and warm environments without performance degradation due to condensation, fogging and frost, especially formed on a protective window on the cordless reader.
2. Description of the Related Art
Electro-optical readers, such as bar code symbol scanners and solid state imagers, have found wide acceptance in retail, wholesale, industrial and military applications. The scanner typically illuminates a symbol comprised of regions of different light reflectivity, senses light of different intensity scattered from the symbol regions, and determines widths and spacings of the symbol regions to derive information encoded in the symbol. The imager determines the widths and spacings of the symbol regions by capturing and processing an image of the symbol. In both types of readers, light passes through a protective window.
Under certain operating conditions, the window can become fogged, or even frosted, and condensation can form not only on the window, but also on the internal electro-optical components of the reader. A cordless reader is often used within indoor refrigerated environments, such as a commercial freezer or a non-heated warehouse, or in outdoor cold environments, such as a ski resort or an oil rig. Condensation forms due to vaporized water droplets in the ambient air within the reader when the reader is moved from such a cold environment into a warm environment. Condensation on the interior surface of the window cannot be wiped away. Light passing through condensation on the window can disable the reader by altering the light. Condensation on the interior optical components likewise alters the light. Condensation on the interior electrical components can cause short circuits and catastrophic failure of the reader. Frost can occur when the reader remains in a cold environment.
The prior art has proposed, for example, in U.S. Pat. No. 5,508,505, a heated chamber in which a scanner is housed until its removal prior to reading a symbol. The art has also proposed, for example, in U.S. Pat. Nos. 5,729,003 and 6,612,493, mounting a heater inside a scanner. The heater includes a resistive element that draws a large quantity of electrical current. If the electrical current is supplied by a power source on the scanner, then the power source is rapidly depleted and must be frequently renewed. If the electrical current is supplied by a power source external to the scanner, then an electrical power cable must be connected between the external power source and the scanner. However, the permanent connection of a power cable is disadvantageous for those applications where full freedom of portability for the scanner is desired.